This photo, provided by the Korea Meteorological Administration, shows the epicenter of a 2.3 magnitude natural quake that hit near North Korea's nuclear testing site in Kilju on Monday. (KMA)

A natural earthquake struck near North Korea's nuclear test site again Tuesday, South Korea's weather agency said, marking the fourth quake to hit the region in just five days.

The 2.5 magnitude quake struck about 38 kilometers north-northwest of Kilju, North Hamgyong Province, at 6:52 a.m., the Korea Meteorological Administration (KMA) said.

"It has been analyzed as a natural earthquake," an agency official said.

The epicenter was at a latitude of 41.29 degrees north and a longitude of 129.23 degrees east at a depth of 29 km, according to the KMA.

The latest quake followed two mild ones, both at 2.3 magnitude, on Monday and another at 3.1 magnitude Friday. All were natural quakes. (Yonhap)